Purification of boron nitride multiwalled nanotubes.

Purification of arc-discharge grown multiwalled boron nitride nanotubes (BN MWNTs) was possible using a simple solubilization and filtration method. Using the common method of arc-discharge with h-BN/Ni/B packed molybdenum tube and a water cooled copper cathode, results in a mixture of hexagonal boron nitride, metal catalyst and boron nitride nanotubes. We show that a simple purification based on the use of surfactants that provide sufficient solubilization for solution filtering of the other materials results in highly purified BN MWNTs. The purified samples were characterized by transmission electron microscopy and scanning tunneling spectroscopy and microscopy. We observed in the purified BN MWNTs square and triangular tube ends, characteristic for this type of nanotube with no metal observed at the tips. Tunneling spectroscopy measurements showed an averaged band gap of approximately 5 eV with the band gap values independent of tube chirality and diameters.